This invention relates to laser printers and more particularly to methods of manufacturing, calibrating, and remanufacturing laser printer cartridges.
The construction and operation of the print engine of a typical laser printer is shown in FIG. 1. Laser printers typically convert a laser signal 10 to a printed image by creating a latent image on a laser-sensitive-photosensitive drum 20 and developing the latent image into a visible image by applying toner powder to the latent image. The toner is transferred from a toner reservoir 30 to photosensitive drum 20 by a developer cylinder 40.
The photosensitive drum 20 is typically an extruded aluminum cylinder. In operation, the surface of the photosensitive drum carries a negative charge. The exterior surface of the photosensitive drum 20 is coated with a layer of an organic-photoconductive material (OPC). The OPC material acts as a photodiode; when exposed to light it becomes electrically conductive in one direction. The photosensitive drum 20 is electrically connected to ground in such a way that charge deposited on exposed portions of the surface of the drum can be conducted from the OPC layer, to the photosensitive drum, and to ground. When a region of the surface of the photosensitive drum 20 is illuminated it becomes conductive and charge is drained from that region (to ground). Areas on the surface of the photosensitive drum 20 which are not illuminated by the laser do not become photoconductive. In typical applications, the charge at a point on the surface which has not been illuminated is -600 V and the charge at a point which has been illuminated is -100 V. The difference in charges over the surface of the drum form a latent image.
The latent image on the surface of the photosensitive drum 20 is developed into a visible image by the application of toner to the laser-exposed regions of the photosensitive drum 20 by the developer cylinder 40. The developer cylinder 40 functions as a valve which regulates the transfer toner from a toner tank or reservoir 30 to the photosensitive drum 20. The developer cylinder 40 generally includes a rotating metallic sleeve 50 with a fixed magnetic member 60 positioned coaxially within the developer cylinder. The developer cylinder is positioned adjacent the photosensitive drum, with its axis parallel to that of the photosensitive drum. A toner cavity or reservoir is positioned adjacent to the developing cylinder 40. The toner generally consists of a fine powder of composite particles. The composite particles include a black plastic resin in which smaller particles of iron are encapsulated. As a point on the surface of the developer cylinder sleeve 50 rotates past the toner supply the magnetic member disposed within the rotating developer cylinder sleeve 50 attracts toner particles onto the surface of the developer cylinder sleeve 50. The depth of the layer of toner on the developer cylinder sleeve 50 is often controlled by a height-control metering blade 70, the gap between the blade and the surface of the developer cylinder controlling the thickness of the toner layer developer sleeve 50.
The developer cylinder 40 is connected to a negative power supply and thus the toner particles on the developing cylinder 40 acquire a negative surface charge. This charge is such that, as the developer cylinder sleeve 50 rotates and brings toner particles into close proximity to the photosensitive drum 20, the particles are attracted to the areas of the photosensitive drum which have been exposed (these areas have a charge of -100 v) and repelled from the areas which have not been exposed (these areas have a charge of -600 v). Transfer of the toner particles is further assisted by applying an AC potential to the developer cylinder 40. The AC potential contributes to overcoming the attraction between the toner particles and the internal magnetic member 60 of the developer cylinder 40 and helps to pull toner on the unexposed areas of the photosensitive drum 20 back to the developer cylinder. A visible image, formed by adherence of toner particles to illuminated areas of the photosensitive drum 20, is thus formed.
The visible image formed on the photosensitive drum 20 is then transferred to paper. Paper, traveling at the same speed at which the surface of the photosensitive drum 20 is rotating, is brought into contact with the photosensitive drum by pickup roller 80 and feed rollers 90. A transfer corona assembly 100, the long axis of which is parallel to the axis of the photosensitive drum 20, is positioned such that the paper passes between the photosensitive drum 20 and the transfer corona assembly 100. (A corona element ionizes the air surrounding it. Ionized air is a conductor of electricity thus the ionized region, or corona, allows a positive charge to migrate to the surface of the paper.) The transfer corona wire 105 produces and deposits a strong positive charge on the back of the paper (the surface not in contact with the pd). This positive charge results in the transfer of the negatively charged toner particles from the photosensitive drum 20 to the paper. As the paper and drum continue to move, the paper peels away from the photosensitive drum 20 and is fed by feeder 110 to a fusing station 120 where the toner is melted and forced into the paper by heat and pressure rollers 125.
After transfer of the image to the paper the rotation of the photosensitive drum 20 carries the region of the surface which has transferred its toner to paper to a cleaning station 130. The cleaning station prepares the surface of the photosensitive drum 20 for a new image. Leftover toner is removed by a urethane cleaning blade 140 which scrapes toner from the photosensitive drum 20 into a waste cavity 150. A sweeper blade 160 in the waste cavity 150 sweeps toner away from the area near the photosensitive drum 20. Erase lamps 170 electrostatically clean the photosensitive drum 20 by illuminating the OPC to neutralize residual charge.
Further rotation of the photosensitive drum 20 brings the cleaned surface to a conditioning station 180. Conditioning consists of the application of a uniform negative charge of -600 V on the surface of the photosensitive drum 20. This charge is deposited on the photosensitive drum 20 by the primary corona assembly 190. The primary corona assembly is positioned with its long axis parallel to the axis of the photosensitive drum 20.
The photosensitive drum 20, developer cylinder 40, toner, toner cavity 30, toner height metering blade 70, cleaner blade 140, waste cavity 150, and primary corona assembly 190 are often contained in a single module referred to as a developer of laser printer cartridge 200. The laser printer cartridge 200 is easily removed and replaced and contains the components most subject to wear or depletion, e.g., the photosensitive drum 20, developer cylinder 40, and toner.